Digestion And Enzymes.

Question 1

What is an enzyme?

Answer 1

Proteins that act as biological catalysts, meaning they speed up reactions without being used up.

They are specific to one type of molecule.

Question 2

What is the name of the molecule that enzymes work on?

Answer 2

The substrate.

Question 3

What are the molecules formed by an enzyme reaction called?

Answer 3

Products.

Question 4

What is the connection point between an enzyme and substrate called?

Answer 4

The active site.
The active site and the substrate are complementary in shape, so they only work on one type of molecule.
This is the “Lock and key model”

Question 5

What is formed when an enzyme and substrate collide?

Answer 5

Enzyme-substrate complex
It is in this complex where the reaction takes place.

Question 6

List 4 different enzymes, their substrate and the reaction products.

Answer 6

Carbohydrase Carbohydrate Simple sugar, glucose

Amylase Starch Simple sugar, glucose

Protease Protein Amino acid

Lipase Fat (Lipid) Glycerol and fatty acids

Question 7

What molecules reduce the rate of reaction and how do they do this?

Answer 7

Inhibitors.
They fit loosely or partially in the active site of the enzyme, which means substrate molecules cannot enter, which leads to a reduced (inhibited) rate of reaction.

Question 8

How does temperature affect enzyme activity?

Answer 8

At low temperatures, the enzyme and substrate molecules have reduced kinetic energy and move slowly, resulting in few collisions between them.

At higher temperatures the enzyme and substrate molecules have increased kinetic energy, increasing the number of collisions and the rate of activity.

This works up to a certain point called the optimum. Once temperatures exceed the optimum, enzyme activity decreases sharply. This is due to an irreversible change in the shape of the enzymes active site, known as denaturation.

Question 9

What is a thermostable enzyme?

Answer 9

They work at a wide range if temperatures.

Question 10

How does pH affect enzyme activity?

Answer 10

Most enzymes only work at a specific pH range. Deviating from the optimum pH will cause the active site to become denatured.

Question 11

How does Enzyme concentration effect the rate of reaction?

Answer 11

The higher the enzyme concentration the more likely a substrate and enzyme will collide, increasing the rate of reaction.

This occurs up to a certain point, after which enzyme activity plateaus as there aren’t enough substrate molecules to react with the extra enzymes.

Question 12

What is the definition of digestion?

Answer 12

The breakdown of large, complex, insoluble molecules into small, simple, soluble ones.

Question 13

What is the the function of the ileum?

Answer 13

Although the final stages of digestion take place in the small intestine, the main function of the ilium is the absorption of digested food products.

Question 14

What are some adaptations for the ileum?

Answer 14

Large surface area due to being long and folded

Thin so digested food products doesn’t have to travel far to reach the blood.

Permeable so digested food can pass through easily

Good blood supply to maintain the concentration gradient for diffusion between the ileum and bloodstream.

Villi finger like projections that further increase surface area.

Question 15

What are some adaptations of the villus?

Answer 15

Good blood supply. A villus has a large network of capillaries for transporting food products.

Lacteal. A tube that absorbs the products of fat digestion before returning them to the blood.

Single layer of surface epithelium cells, i.e. walls only one cell thick, reducing the diffusion distance.

Permeable, so digested food products can pass through easily.

Question 16

What are carbohydrates?

Answer 16

Carbohydrates provide energy.
There are two types, simple and complex

Simple carbohydrates are sugars, like glucose and lactose. They are a fast acting source of energy.

Complex carbohydrates are a slow release of energy, like cellulose, starch and glycogen. They are long chains of sugars.

Learn the diagrams of these molecules.

Question 17

What are lipids?

Answer 17

Fats.
Fats are a store of energy, providing double the energy that carbohydrates and proteins do.
They are made up of fatty acids and glycerol.

Learn the diagram for these molecules.

Question 18

What are proteins?

Answer 18

Protein is used for the growth and repair of cells.
It can be used as a source of energy if carbohydrate and fat reserves are low.

They are made if long chains of amino acids.

After digestion amino acids are absorbed into the bloodstream and brought to cells that reassemble them into proteins needed by the body.

Learn the diagrams for these molecules.

Question 19

How do you test for sugar?

Answer 19

Benedict’s reagent.

Add the reagent to the food and boil in a water bath.
The reagent will start blue, and a positive result will turn brick red.

Question 20

How do you test for starch?

Answer 20

Iodine.

Add iodine reagent to the food.
The reagent will start yellow brown, but a positive result will turn it blue-black

Question 21

How do you test for protein/amino acid?

Answer 21

Biuret.

Add biuret reagent to food.
It will start blue, and a positive result will turn it lilac/purple

Question 22

How do you test for fat?

Answer 22

Ethanol.

Add ethanol to food to dissolve the fat then add water.

It will start colourless, but a positive result will turn it cloudy white.

Question 23

What three elements are found in all biological molecules?

Answer 23

Carbon
Hydrogen
Oxygen

Question 24

What are some modern uses for enzymes?

Answer 24

Washing powders- to remove stains.

Question 25

How do you calculate the energy that a food contains?

Answer 25

Burning food experiment:

1. Measure 20cm3 of water into the test tube.
2. Clamp the test tube in the retort stand at an angle, over a heat resistant mat.
3. Weigh a small piece of food and record the mass.
4. Take the temperature of the water and record it in the table.
5. Fix the food at the end of the mounted needle.
6. Ignite the food using the end of a Bunsen burner, and immediately hold it about 1cm below the test tube and above a heat resistant lamp. If the flame goes out, quickly relight it.
7. When the food stops burning, gently stir the water with the thermometer and record the temperature.
8. If there is a significant amount of unburied food left on the needle, reweigh this and record the mass remaining.
9. Empty the test tube and refill it with another 20cm3 of cold water. Repeat the experiment using a different food.
10. Repeat each of your chosen foods in order to calculate an average.
11. Calculate the amount of energy using the equation below:

Volume of water x temp increase x 4.2
——————————————————
Mass of food

Question 26

What experiment allows you to show the effects of changing temperature and pH on enzymes?

Answer 26

1. Set up water baths at various temperatures (e.g. 0°C, 20°C, 40°C, 60°C and 80°C).
2. Add starch solution to 5 test tubes.
3. Add amylase solution to another 5 test tubes.
4. Place one starch and one amylase test tube into each water bath for 5 minutes - to allow
   the enzyme and substrate to reach the desired temperature.
5. Place 1 drop of iodine into each dimple on a spotting tile.
6. Add the amylase to the starch in the 0°C water bath.
7. Start the timer.
8. Every minute remove a sample of the starch-amylase solution and add it to a drop of iodine on the spotting tile.
9. Repeat step 8 until the iodine no longer changes colour - meaning that there is no starch present, in other words the amylase has broken all starch down.
10. Repeat steps 6-9 for each of the temperatures.
11. Record results.
12. Draw a graph to show the time taken for starch to be digested at different temperatures.